Friction welding method

ABSTRACT

Friction-welding apparatus comprising a rack and pinion for translating force from a unidirectionally, linearly acting hydraulic motor into rotational force and applying the resultant rotational force to one of a pair of relatively rotatable weld pieces. Programming means regulate operation of the hydraulic motor to precisely determine energy input to a weld interface between the weld pieces.

United States Patent 1 1 3,720,993 Farmer et al. 1March 20, 1973 [54]FRICTION WELDING METHOD 3,420,428 1/1969 Maurya et a1. ..228/2Inventors: Charles G. Farmer, Edelstein; Cab 3,469,300 9/1969 Nagiri..228/2X vin D. Loyd, Peoria, both Of Ill. OTHER PUBLICATIONS [73]Assignee: Caterpiller Tractor Co., Peoria, Ill. Strapping Weld byFriction, Iron Age July 7 1966 22 Filed: on. 26, 1970 [21] Appl' 84139Primary Examiner-J. Spencer Overholser Related Application DataAssistant Examiner-Robert J. Craig Attorney-Fryer, Tjvensvold, Feix,Phillips & Lempio [62] Division of Ser. No. 728,646, May 13, 1968, Pat.No.

356110 57 ABSTRACT [52] US. Cl. ..29/470.3, 156/73, 228/2Frictiomwelding apparatus comprising a rack and [51] Int. Cl. ..B23k27/00 pinion for translating force from a uniclirectionally FieldSearch-W228; linearly acting hydraulic motor into rotational force74/109 and applying the resultant rotational force to one of a pair ofrelatively rotatable weld pieces. Programming [56] References cued meansregulate operation of the hydraulic motor to UNITED STATES PATENTSprecisely determine energy input to a weld interface between the weldpieces. l,95l,906 3/1934 Hansen ..74/l09 3,002,871 10/1961 Tramm et a1..228/2 5 Claims, 6 Drawing Figures |6 I6 36 23 s illll @1251, 38'llllllllllllll mumnnumlluufifi h $imilmfi IIIIIIIIIIIIIIIIIII}\\\\\\.zmi 26 4| ll:- 32

PATENTEDMARZU I975 3, 720.993 SHEET 1 [IF 3 I N VEN TORS CHARLES G.FARMER CALVIN D. LOY'D FRICTION WELDING METHOD This is a division ofapplication Ser. No. 728,646 filed May 13, 1968, now Pat. No. 3,567,100.

BACKGROUND OF THE INVENTION Friction welding is broadly comprised ofpressing two weld pieces together at a common interface under suitablepressure and urging them into relative motion to develop frictionalcontact at their interface. By means of the frictional contact, heat isgenerated at the interface to effect a plastic we'ld condition. Theenergy content, which may be broken down into the duration and rate ofenergy transmission to the interface to form a suitable bond, isselected according to criteria which are well known in the prior art.Among prior art procedures, conventional friction welding generallyrefers to a process where one of the weld pieces is relatively rotatedwhile in contact with the other weld piece under a load axial to theirinterface. The speed of rotation may be generally constant with theduration of the relative rotation selected to determine the energyprovided at the interface. Inertial welding is a variation of the aboveprocess in that prior to axial engagement, one of the weld pieces isrotated to a predetermined speed in association with a selected inertialmass. The other weld piece is typically secured against rotation andbrought into frictional engagement with the rotating weld piece at acommon interface. At least a predeterminable portion of the inertialenergy in the rotating weld piece and associated inertial mass is thustransferred to the interface of the weld pieces to condition it forbonding. This process is generally characterized by a relatively highinitial rate of rotational speed between the weld pieces whichdiminishes during the welding process. This process is particularlyeffective in many applications since the high initial rate of relativerotation quickly heats the interface to a suitable plastic conditionandis followed by prolonged relative rotation at lower rates whichiseffective for plastic working of material at the interface which issusceptible to grain growth to refine the grain. The amount and rate ofenergy to be transferred to the interface varies, for example, with thecomposition, configuration and mass of the weld pieces. Either of theabove processes may be particularly effective for a given combination ofsuch characteristics. However, both processes are usually performed withequipment including a motor applying rotational drive to one of theweldpieces. Generally complex equipment is provided to control criticalwelding parameterssuch as the duration and rate of relative rotation,etc.

Reciprocable welding is another type of process where one weld piece iscaused to move relative to the other weld piece generally in areciprocating or backward and forward fashion. This process is employed,for example, where the weld piece configuration does not permit relativerotation. Otherwise, the process. generally involves the sameconsiderations as to the amount and rate of energy transfer to the weldinterface, etc.

The apparatus and methods of operation for each of the above processesare not always readily adaptable to a wide variety of weldingconditions. Complex componentry and controls to make these processesmore versatile also tend to increase capital costs and complexity ofoperation. Accordingly, it is desirable to provide novelfriction-welding apparatus and methods of welding which permit the useof simplified components and which are readily adaptable to a widevariety of friction welding applications.

SUMMARY OF THE INVENTION The present invention fulfills the above needsby employing friction welding apparatus in which drive means areeffective to produce a precisely controlled, limited amount ofunidirectional, linear motion during the welding portion of each weldcycle to set the weld pieces in relative motion under pressure toachieve bonding. Translating means translate the unidirectional, linearmotion into suitable motion such as rotation or reciprocable motionwhich is applied to the weld pieces in order to set them into relativemo tion and develop frictional contact at their interface suitable forbonding. The translating means are preferably a rack and pinion assemblyfor setting the weld pieces into relative rotation.

Programming means are preferably associated with the drive means toselectively regulate energy delivered to the weld interface.

A preferred mode of operation within the present invention comprises thestep of pressing two weld pieces together at a common interface anddriving them in rubbing contact with drive or motor means of the typedescribed immediately above.

Accordingly, it is an object of the invention to providefriction-welding apparatus effective to produce a precisely controlled,limited amount of unidirectional, linear motion-during the weldingportion of each weld cycle for moving two weld pieces in relativemotion.

It is another object to provide programming means for preciselyregulating energy delivered to the interface of the weld pieces foreffecting a suitable bond. The programming means are preferablyeffective to simulate conventional friction welding or inertial weldingtechniques or to provide varied parameters as dictated by particularwelding applications.

It is another object to provide a method of pressing two weld piecestogether and driving them in rubbing contact by motor means effective toproduce a precisely controlled, limited amount of unidirectional,linear.

' motion during the welding portion of each weld cycle.

Thus, the present invention permits precise regulation of criticalwelding parameters and particularly of the rate and duration of energydelivery to an interface between two weld pieces. Since the drive ormotor means produces unidirectional, linear motion for setting theweldpieces in relative motion, both the duration and rate of the motionproduced by the motor are susceptible to very precise regulation orprogramming. Since these characteristics determine the rateand durationof energy consumption at the weld interface, the invention permitsselective regulation of welding parameters precisely suited to variouswelding applications. These same characteristics also determine thetotal amount of relative motion between the weld pieces. Thus,.theinvention also permits very precise angular alignment of the weld piecesat completion of a weld cycle. Alignment of the welded pieces is oftennecessary and sometimes of critical importance in certain applicationsso that versatility of the present welding apparatus and method isfurther extended. With a rack and pinion employed to translate theunidirectional, linear motion into relative rotation of the weld pieces,the characteristics of rate and duration may both be preciselyestablished through selection and close regulation of the distancethrough which the motor and rack are operable or of the number of turnsto be experienced by the pinion during the welding portion of each weldcycle.

Other objects and advantages are made apparent in the followingdescription having reference to the accompanying drawings wherein:

FIG. 1 is a side elevation view, with parts in section, of afriction-welding machine incorporating apparatus of the presentinvention and for practicing the welding method of the invention;

FIG. 2 is a block diagram of programming means for regulating operationof the apparatus of FIG. 1;

FIG. 3 is a schematic representation of hydraulic control means for usein conjunction with the programming means of FIG. 2;

FIG. 4 is a block diagram of alternate programming means for regulatingoperation of a welding machine generally similar to that shown in FIG. 1to selectively vary welding speed as well as duration during each weldcycle; and

FIGS. 5 and 6 are schematic representations of hydraulic drive andalternate hydraulic control means respectively for use in conjunctionwith the alternate programming means of FIG. 4.

A friction-welding machine is illustrated in FIG. 1 for the bonding oftwo weld pieces 11 and 12. In accordance with conventional practice, theweld pieces are to be urged together under suitable pressure loadingwith their adjacent surfaces forming an interface for bonding. The weldpieces are placed in relative motion to develop frictional contact attheir interface. By means of this frictional contact and by controllingthe relative motion of the weld pieces, a selected quantity of energy istransferred to the interface to achieve suitable bonding temperature orplastic condition and for plastic working of material at the interfacewhich is susceptible'to grain growth'to refine the grain. The energycharacteristics required at the interface are of critical importance andvary substantially with composition, shape and mass of the weld pieces,for example. For different weld piece compositions, different bondingtemperatures are required along with widely varying amounts of plasticworking. In some applications, very little if any additional working isrequired after the appropriate bonding temperature is reached. Therelative motion of the weld pieces may take any of numerous forms, forexample, rotating or reciprocating motion.

The method ofimparting relative motion to the weld pieces may similarlyvary. For purposes of describing a specific embodiment, one of the weldpieces 11 is secured against rotation by a conventional tailstock chuck13 which is supported on a cross member 14. The cross member is slidablymounted on risers 16 for axial motion relative to the other weld piece12. The risers are mounted in turn on a base structure 17. Pressureloading means which may comprise an air cylinder 18 are mounted on therisers and are coupled with the cross member for urging the weld piecesinto engagement at their interface under selected pressure.

The other weld piece is mounted for rotation upon a spindle chuck 19which is rotatable along with itssupporting spindle shaft 21 on bearings22. Application of suitable rotational force to the weld piece 12, withthe cylinder 18 being extended to properly urge the weld pieces intopressure engagement, transfers energy to their interface as necessaryfor bonding.

For the application of resultant or rotational force to the weld piece12, motor or drive means such as the double-acting hydraulic cylinder 23are operable under precise control for providing unidirectional, linearmotion during the welding portion of each weld cycle to set the weldpieces into relative motion for bonding as described above. In theillustrated embodiment, introduction of fluid under pressure to the headend of the cylinder through a conduit 24 causes its rod 26 to extend (orretract) during each weld cycle to provide the unidirectional, linearmotion.

Means for translating the linear motion into suitable resultant orrotational force for application to the weld piece 12 are provided by arack 27 and pinion 28. Regulation of the rate of fluid flow from thepump to the cylinder provides rectilinear motion in the rod 26 whichestablishes appropriate rectilinear velocity for a particular weldingapplication. That motion is simultaneously translated into rotationalmotion and applied to the weld piece 12 by the rack and pinion to effecta bond between the weld pieces.

Since it is necessary to cause very rapid extension of the cylinder 23for many welding applications, some means are necessary to snub the rodas it approaches its fully extended position to avoid damage to thehydraulic circuitry or mechanical components. Such means could beincluded in the programming and control apparatus described below.However, those means may be simply embodied in the reduced cylindricalportion 36 at the rod end of the cylinder 23 and the cylindrical portion37 of mating diameter mounted on the rod adjacent its piston 38. A fluidconduit 39 between the valve 34 and rod end of the cylinder iscommunicated with the reduced cylindrical portion 36. As the rod 26approaches its fully extended position, the cylindrical portions 36 and37 isolate the conduit 39 and form a closed chamber within the cylinderwhich is communicated to drain through a relief valve 41. Risingpressure in the closed chamber resists extension of the rod and providesa cushioning effect as the increasing fluid pressure is relieved by thevalve 41. The control valve 34 may be repositioned to direct fluid underpressure to the rod end of the cylinder to retract the rod and reset therack and pinion for a new welding cycle.

As discussed above, the amount of energy and the rate at which it istransferred to the weld interface are examples of parameters which areparticularly determinative of the characteristics of a bond formed byfriction welding. Prior art experience indicates that it is oftendesirable to preselect such parameters to simulate conventional frictionwelding and inertial welding techniques. It is additionally desirable tobe able to freely and independently select these parameters foroptimizing bond characteristics in still other applications. It isapparent that the apparatus described above is particularly adaptable toprogramming of the necessary parameters.

Accordingly, programming means are provided for controlling parameterssuch as those described above to thereby regulate the energy transferredto the interface from the motor means.

One embodiment of such programming apparatus is illustrated in FIG. 2and, together with hydraulic control apparatus illustrated in FIG. 3,provides for substantially constant speed operation of the hydraulicmotor of FIG. 1 to generally simulate conventional friction weldingtechniques, for example. Components in FIGS. 2 and 3 which are identicalwith components described above with reference to FIG. 1 are identifiedby the same numerals.

In this embodiment, the control valve 34 is operable in three positions:a weld position 51 wherein fluid from the pump 33 is directed to thehead end of the cylinder 23 for extension of its rod and initiation of awelding cycle; a Reset position 52 wherein fluid is directed to the rodend of the cylinder for retraction of the rod and repositioning of therack and pinion between cycles; and a central Off position 53 whereinthe pump 33 is isolated from the cylinder. The control valve is normallyspring-centered at its Off position 53. A first solenoid 54 is operablein response to an appropriate electrical signal to reposition thecontrol valve to its Weld position 51. A second solenoid 56 is similarlyoperable in response to an electrical signal to reposition the controlvalve to its Reset position 52. The spring-centered control valve isalways returned to its Off position 53 when both of the solenoids aredeactuated.

A three-position selector switch 57 is electrically coupledwith thesolenoids 54 and 56 to control their operation as discussed in greaterdetail below. The switch is operable to its Off or Reset position inresponse to actuation of a cam 58. The cam 58 is associated with therack 27 to be actuated as the rack is extended by the motor to indicatecompletion of a weld operation. The switch is also operable to its Offposition from its Reset position in response to actuation of anadjustable cam 59. The cam 59 is also associated with the rack 27 to beactuated as the rack is retracted to properly positionthe motorcomponents and rack for commencement of a new weld cycle. As theadjustable cam 59 is linearly repositioned relative to the rack, itvaries the starting positions of the motor components and rack to alterthe distance through which the rack is operable by the motor. Thus,adjustment of the cam 59 permits selective regulation not only ofwelding speed but also permits additional variation of the quantity ofenergy to be transferred to the weld interface.

The selector switch 57 is also coupled to a third solenoid 61 whichoperates a valve 62. The valve 62 is associated with the pressureloading cylinder 18 so that propriate force for welding. A fluidaccumulator (not shown) may be associated with the pump 33 to store aquantity of fluid under a given pressure to insure an adequate supplyfor whatever speeds are required-of the hydraulic motor 23. Theaccumulator also allows the use of a smaller pump and can be chargedbetween cycles while the weld pieces are being removed and new piecesinserted into the machine. A pressure relief valve controls the chargein the accumulator. In such a case, a variable flow control valve iscommonly located in the circuit downstream of the accumulator permitcontrol of the motor velocity. The cam 59 is positioned to provide foroperation of the motor and rack through a selected linear distance.Actuation of the selector switch 57 to its Weld position energizes thesolenoid 61 for pressure loading of the weld pieces, then energizes thefirst solenoid 54, positions the control valve 34 to its Weld position51 and causes the motor 23 to initiate a weld cycle. As the rack isfully extended by the motor and the welding operation approachescompletion, the cam 58 is actuated to reposition the selector switch 57to Off. The bonded weld pieces are removed, the selector switch ispositioned at Reset for commencement of a new weld cycle and new weldpieces are inserted in the chucks 13 and 19 prior to repetition of theabove steps to initiate a new weld cycle. Inthis embodiment, theadjustable cam 59 could be omitted. The distance through which the motorand rack are operable could be similarly regulated by providing forlinear adjustment of the cam 58 to varythe linear point at which a weldis completed.

In some welding applications, where it is desirable to simulate inertialwelding techniques, for example, it is necessary in addition toselectively regulate the welding speed or relative rotation of the weldpieces during each welding operation. Programming and control meanspermitting selective speed variation during a welding operation aredescribed with reference to FIGS. 4, 5 and 6. Components which aresimilar to those described with reference to FIGS. 1 3 are identified bysimilar primed numerals. To permit selective variation of welding speedduring a weld operation, a hydraulic pump 101 is connected to both thehead and rod ends of the double acting hydraulic cylinder 23' as will bediscussed in greater detail below with reference to FIG. 5. The pump 101is of a conventional type having a reversible and adjustable cam 102.Proper positioning of the cam permits regulation of fluid flow to eitherend of the motor 23' or complete termination of fluid flow to the motor.Thus, selective operation of the cam 102 may provide for initiation andtermination of each weld cycle as well as for variable rate operation ofthe motor. Accordingly, the adjustable cam provides for continuousadjustment of the rate of relative motion between the weld pieces andmore critical regulation of energy provided to the weld interface.

Selective positioning of the cam 102 is provided by a control motor suchas a double-acting hydraulic cylinder 103 having a neutral positioncorresponding to termination of fluid flow through the pump 101.Actuation of the control motor in one direction, for example, extension,conditions the adjustable cam pump 101 for extension of the motor 23 toinitiate a weld cycle. Operation in the other direction, 'thatis,retraction, also causes retraction of the motor 23' to reset the motorand rack 27 (see FIG. 1) for a new weld cycle. Operation of the controlmotor 103 is in turn regulated by a servo-operated valve 104 as isdiscussed below.

A programmer 106 is of a type suitable to regulate an entire weld cycleby controlling the servo valve 104. For example, it may be of anumerical control type capable of being programmed to carry out thewelding operation. The programmer in combination with two summingjunctions 107 and 108 and two transducers such as a DC tachometer 109and a linear potentiometer 111 serves to regulate instantaneous weldingspeed and duration by controlling the cam pump 101 through the servovalve 104 and control motor 103. The programmer continuously generatesan electrical signal during a welding cycle which signal isrepresentative of desired instantaneous speed of rotation of the weldpiece 12' relative to the other weld piece 11'. The DC tachometer 109senses actual rotational speed of the weld piece 12' and generates asignal representative of that actual speed. Both the actual and desiredspeed signals are received by the first summing junction 107 whichresponds by generating a differential signal representative ofinstantaneous speed change. The differential speed signal is furtherrepresentative of a desired position of the pump cam 102 to accomplishthe necessary change in welding speed. The potentiometer 111 isassociated with the control motor or cylinder 103 to sense the actualposition of the pump cam which is determined by the degree of extensionor retraction of the cylinder 103. The signals representative of actualand desired pump cam position are received by the second summingjunction 108 which responds by generating a differential signalrepresentative of the necessary change of pump cam position. Thatdifferential positioning signal is received by the servo valve 104 whichresponds to instantaneously position the pump cam to continuallyregulated welding speed at the rate established by the programmer. Sincethe pump cam is reversibly and variably operable, it is apparent thatthe programming and control apparatus described above is effective toregulate the entire weld cycle including initiation, control of energyinput to the weld interface and termination. As with the embodimentdescribed with reference to FIG. 2, the programmer 106 is also coupledwith the solenoid valve 61' to selectively regulate axial pressureloading at the interface of the weld pieces. Having reference to FIGS. 6and 4, the servo valve 104 is a three-position valve similar to thecontrol valve 34 of FIGS. 2 and 3. Fluid under pressure is delivered tothe control cylinder 103 from a pump 112 and a fluid pressureaccumulator 113 to insure delivery of constant pressure to the controlcylinder for precise positioning of the pump cam 102.

Referring to FIG. 5, the hydraulic drive arrangement between the pump101 and motor 23' includes conduits 114 and 116 communicating the sidesor manifolds 117 and 118 of the pump 101 with the head and rod ends ofthe cylinder 23', respectively. Since the pump 101 is reversiblyoperable, its manifolds 117 and 118 will alternate between high oroutput fluid pressure and low or inlet fluid pressure. A replenishingpump 119 is in communication with both manifolds 117 and 118 throughcheck valves 121 and 122, respectively, to insure a constant supply offluid in the low-pressure manifold. Thus, the replenishing pump preventscavitation in the pump 101 and provides for accurately controlledoperation of the motor 23. The replenishing pump 119 is a fixeddisplacement pump which supplies fluid to make up any leakage and alsomaintains the desired pressure on the low-pressure side of the circuit.The excess flow from the replenishing pump 119 passes over the lowpressure relief valve 126. A two-position hydraulically responsiveshuttle valve 123 also selectively communicates the manifolds 117 and118 with either high pressure or low pressure relief valves 124 and 126,respectively. The shuttle valve is operable to insure that the lowpressure manifold is communicated to the low pressure relief valve andthe high pressure manifold is communicated to the high pressure'reliefvalve for proper operation and protection of the hydraulic circuit.

Thus, the present invention provides a novel friction welding machine towhich simple programming means are adaptable to provide accurate energycontrolfor a wide variety of welding applications.

What is claimed is:

1. In a method of the kind in which two metal weld pieces are bondedacross a common interface while the pieces are relatively moved inrubbing contact until their interface is brought to a plastic condition,the steps comprising pressing the pieces together at their interface,

driving the pieces in rubbing contact by motor means effective toproduce a precisely controlled, limited amount of unidirectional, linearmotion during the welding portion of each weld cycle, and

translating the unidirectional, linear motion of the motor means intoreciprocating motion for application to weld pieces to set them intorelatively reciprocating motion.

2. In a method of the kind in which two metal weld pieces are bondedacross a common interface by pressing the pieces together at theinterface while the pieces are relatively moved in rubbing contact untiltheir interface is brought to a plastic condition, the steps comprisingpressing the pieces together at their interface,

driving the pieces in rubbing contact by motor means effective toproduce a precisely controlled, limited amount of unidirectional,.linearmotion during the welding portions ofeach weld cycle, and translatingthe unidirectional, linear motion of the motor means into rotationalmotion for application to the weld pieces to set them into relativelyrotating motion. r

3. The method of claim 2 wherein the step of translating unidirectional,linear motion into rotational motion is accomplished by means of a rackand pinion.

4. The method of claim 1 further comprising the step of selectivelyprogramming the unidirectional, linear motion of the motor means toprecisely regulate energy input to the interface of the weld pieces.

5. The method of claim 4 wherein the step of selectively programming theunidirectional, linear motion of the motor means is effective toprecisely and selectively regulate rate and duration of relative motionbetween the weld pieces during the welding portion of each weld cycle.

1. In a method of the kind in which two metal weld pieces are bondedacross a common interface while the pieces are relatively moved inrubbing contact until their interface is brought to a plastic condition,the steps comprising pressing the pieces together at their interface,driving the pieces in rubbing contact by motor means effective toproduce a precisely controlled, limited amount of unidirectional, linearmotion during the welding portion of each weld cycle, and translatingthe unidirectional, linear motion of the motor means into reciprocatingmotion for application to weld pieces to set them into relativelyreciprocating motion.
 2. In a method of the kind in which two metal weldpieces are bonded across a common interface by pressing the piecestogether at the interface while the pieces are relatively moved inrubbing contact until their interface is brought to a plastic condition,the steps comprising pressing the pieces together at their interface,driving the pieces in rubbing contact by motor means effective toproduce a precisely controlled, limited amount of unidirectional, linearmotion during the welding portions of each weld cycle, and translatingthe unidirectional, linear motion of the motor means into rotationalmotion for application to the weld pieces to set them into relativelyrotating motion.
 3. The method of claim 2 wherein the step oftranslating unidirectional, linear motion into rotational motion isaccomplished by means of a rack and pinion.
 4. The method of claim 1further comprising the step of selectively programming theunidirectional, linear motion of the motor means to precisely regulateenergy input to the interface of the weld pieces.
 5. The method of claim4 wherein the step of selectively programming the unidirectional, linearmotion of the motor means is effective to precisely and selectivelyregulate rate and duration of relative motion between the weld piecesduring the welding portion of each weld cycle.